The Picornaviridae family includes about 70 distinct serotypes of enterovirus. Clinical manifestations of enterovirus infection range from mild “summer cold” to neurological and cardiovascular disorders.
Enterovirus consists of a simple virus capsid and a single strand of positive sense RNA. The capsid contains four proteins, VP1 to VP4. Variations within capsid proteins VP1 to VP3 are responsible for antigenic diversity among enterovirus, with neutralization sites most densely clustered on VP1 (Rueckert, Virology, Lippincott-Raven, New York, 1990, 507). Replication of RNA viruses is directed by viral RNA polymerase of low fidelity, i.e., an error frequency of 10−3 to 10−4 misincorporated nucleotide per round of replication (Holland et al., Science, 1982, 215:1576–1585; Ward et al., J. Virol., 1988, 62:558–562; and La Torre et al., J. Virol., 1990, 64:664–671). In other words, replication of an enterovirus genome consisting of about 7500 nucleotides results in a population of genomes having on average at least one mutation. Moreover, recombination occurs at a very high frequency in the picornaviruse family (McCahon, Arch. Virol., 1981, 69:1–23).